1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device wherein a metal functioning as a radiator or an electrode is formed on a substrate, and also relates to semiconductor devices manufactured by this manufacturing method.
2. Background Art
Chun-Wei CHANG et al. (JJAP Vol. 46, No. 4A, 2007, pp. 1409-1414) discloses a semiconductor device in which a Cu diffusion blocking layer is formed between a substrate and an overlying Cu layer by a vacuum film-forming method such as vacuum deposition. The vacuum film-forming method can be used to form films of various metals. For example, a Cu diffusion blocking layer may be formed of Ta by a vacuum film-forming method so as to achieve enhanced Cu diffusion blocking effect.
Japanese Laid-Open Patent Publication No. 2011-165810 discloses a technique for forming a Pd plating layer on a GaAs substrate by means of electroless plating. This publication also discloses that a metal layer of Cu, etc. may be formed on the Pd plating layer.
A Cu diffusion blocking layer formed by a vacuum film-forming method as disclosed by Chun-Wei CHANG et al. above tends to exhibit inadequate covering ability (or coverage ratio), since vacuum film-forming techniques are anisotropic. It has been found, particularly, that vacuum film-forming methods cannot form a film having high covering ability on substrates having a projection or recess. If a Cu diffusion blocking layer formed on a substrate has low covering ability, a portion of the Cu layer overlying the Cu diffusion blocking layer will be in direct contact with the substrate, so that Cu in the Cu layer diffuses through that portion into the substrate.
The technique disclosed in the above patent publication has been found disadvantageous in that the Pd plating layer formed by electroless plating does not have adequate Cu diffusion blocking effect, with the result that Cu in the metal layer diffuses into the substrate and thereby affects the characteristics of the semiconductor device.